1. Field of the Invention
This invention relates to a device and a method for insufflating oxygen gas or anesthetic gas such as laughing gas to the respiratory system of a living body in synchronism with his breathing. More particularly, the invention relates to maximization of the effect of gas insufflation by improving of the gas inhalation efficiency so as to be matched in the optimum condition.
2. Related Art Statement
In general, there are two methods for a living body, e.g., a patient, to inhale a gas such as oxygen gas or anesthetic gas; namely, the closed type and the open type. The closed type uses the so-called facemask or an endotracheal tube and supplies the gas to the living body through a breathing circuit system, which includes the respiratory organs of the living body and the gas supply device, while airtightly separating the system from the atmosphere. This closed type method has an advantage in its high inhaling efficiency. However, the closed type method has a shortcoming of causing irritation or discomfort on the side of the patient or the like because of the covering of his mouth and nose air-tightly and the direct insertion of foreign bodies into his trachea. Accordingly, the closed type method has been used mainly for unconscious and seriously sick patients who need artificial and augmented ventilation.
On the other hand, the open type method inserts the tip of a gas supplying tube into the nostril or the mouth of a patient so as to supply the gas while keeping the above-mentioned respiratory circuit system open to the atmosphere. Thus, parts to be in tight contact with the face or upper airway of the patient for making an airtight system are eliminated, and the irritation or discomfort on the side of the patient is reduced and the patient is allowed to speak, eat or drink freely during the inhalation treatment. Accordingly, this open type method is mainly used for mild cases in which self-breathing is possible and dependable.
In the conventional closed type gas-breathing apparatus and method, gas is supplied in response to the breathing of the living body by detecting the gas pressure changes in the closed breathing circuit system. However, in the conventional open type gas-breathing apparatus and method, it is difficult to detect the pressure change in the breathing circuit system, and in most cases, the gas is supplied at a steady flow rate regardless of the breathing of the living body. Thus, the gas is constantly insufflated into the living body even during the exhalation, and discomfort has been cause to him. Besides, a large part of the gas supplied during the exhalation period of the living body is wasted by being discharged to the atmosphere without being used. In addition, the open type gas-insufflation apparatus is susceptible to undue reduction of the concentration of the gas being inhaled because the tip of the gas-supply tube is open and directly communicates with the atmosphere. To cope with such reduction of the gas concentration to be inhaled, it has been practiced to increase the flow rate of the such constantly fed gas.
To overcome such shortcomings, the inventors proposed in their Japanese Patent Laying-open Publication No. 8,972/84 a breath-synchronized open type gas-insufflation system, in which the gas was supplied only during inhalation periods in synchronism with the breath of the living body, and the inventors disclosed that the amount of insufflating gas needed to maintain the equivalent efficiency of oxygenation was greatly reduced. More particularly, the inventors proposed an efficient gas-insufflation by periodically interrupting the gas supply in synchronism with the breaths of the living body so as to insufflate the gas only during his inhalation periods.
In an ideal gas insufflation, the amount of gas to be insufflated should be changed in coincidence with variation of the inhaled air volume in each inhalation, which not only depends on the inherent respiration pattern of the individual living body but also depends on his emotional, intentional and physical conditions. If the amount of the inhaled gas can be controlled in the above-mentioned manner, the gas concentration in the air inhaled into the living body can be always kept at a high level. In readily, however, it is almost impossible to realize the above ideal gas insufflation by accurately measuring the volume of inhaled gas for each living body at each moment and keeping the flow rate of the insufflated gas in good agreement with the measured volume of the inhaled gas, because the respiration pattern varies depending on individual living bodies, and the respiration pattern of a living body is ever changing depending on various physical, intentional and emotional activities on each time of measurement. Thus, there has been a limit in improvement of the gas-insufflation efficiency.
The inventors further suggested in their Japanese Patent Laying-open Publication No. 253,495/1984 a breath-synchyronized concentrated-oxygen supplier which simultaneously improved both the gas (oxygen in the Publication) production (concentrating) efficiency of the oxygen concentrator on the side of a machine and gas-inhalation efficiency on the side of a living body to whom the device feeds the gas. The improvements are based on predetermined of a gas-feeding pattern which matches the average of several respirations immediately before each insufflation, elimination of gas waste by stopping the gas supply at an end portion of each inhalation, and maintenance of a comparatively high gas concentration in the feed gas by alternate use of a pair of oxygen concentrator columns of pressure swing adsorption type. It was noted that the gas inhaled by the living body at the end portion of each inhalation did not reach the effective part of his respiratory organ.
In the previously proposed breath-synchronized gas-insufflation devices, a high gas (e.g., oxygen) concentration is provided at the very beginning of each inhalation and wasteful gas supply at the end portion of each inhalation is eliminated. To maintain the high oxygen pressure, a pair of oxygen concentrator columns of pressure swing adsorption type are alternately used; namely, extracting oxygen from one column while regenerating the other column by purging with the product gas in an alternate manner. However, the previously proposed devices have a problem in that a maximum gas inhaling efficiency on the side of a living body is not always ensured, because the devices failed in providing continuous supply of a sufficient amount of gas at the beginning of each inhalation for matching the high gas inhaling capability available at that moment on the side of the living body.